Barnes et al in U.S. Pat. Nos. 2,975,603; 3,086,370; and 3,217,503 disclosed a process for producing gasified ice products such as carbonated ice which were characterized by high volumes of carbon dioxide and storage lives as long as 33 days. These patents taught that carbonated ice products of this type had the stability to form superior effervescent beverages upon mixture with aqueous liquid. According to one aspect of the disclosure, a carbonated ice was prepared by subjecting aqueous liquid to a carbon dioxide pressure of at least about 200 psig and preferably less than 600 psig; maintaining the aqueous liquid and the carbon dioxide in contact for a time sufficient to permit absorption in the liquid of carbon dioxide in bound form in the formation of ice containing at least about 25 to 27.5 milliliters of carbon dioxide per gram of ice; and withdrawing the carbonated ice from the chamber in frozen form.
The product produced in this manner would typically contain pockets of gaseous and liquid carbon dioxide which caused cracking or explosive failure in water. As a partial remedy to this problem, Barnes et al suggested degassing or stabilizing the product for a period of about 24 hours at about -10.degree. C. They disclosed that during this period, any carbon dioxide which may be loosely held within the product is evolved, and that liquid carbon dioxide would generally volatilize and pass from the solid product. Upon testing, it is disclosed that the degasified carbonated ice produced a vigorous evolution of gas when placed in water. The average bubble size and quantity of bubbles were said to give the resulting beverage the appearance of the familiar "club soda" carbonated drink. Experience has shown, however, that this vigorous evolution typically includes popping and cracking upon placement in water with the resultant splashing of water from the container. Moreover, in order to remove the product from the pressure reactor, it is necessary to chip or chisel the ice out of the reactor vessels, making the production of commercial size quantities extremely difficult, especially where the resulting product is of very uneven dimensions. Attempts to granulate or crush products prepared in this manner also require great amounts of energy and significantly diminish the stability of the resulting product.
U.S. Pat. No. 3,086,370, also to Barnes et al, discloses that in addition to carbon dioxide, gasified ice products containing other gases such as nitrous oxide, certain sulfur-containing gases, certain chlorine-containing gases, various inert gases and carbon monoxide could be formed. Because this patent was based upon a continuation-in-part application of U.S. Pat. No. 2,975,603 (Barnes et al, supra), much of the same disclosure regarding pressures and degasing of the solid ice product is carried forward. Significantly, the produts produced according to this disclosure are also relatively dense solids formed in a reactor which makes removal difficult, and exhibit serious problems of popping and cracking when placed in water.
A similar disclosure is found in U.S. Pat. No. 3,217,503, which again was a continuation-in-part of the application which resulted in the first-mentioned Barnes et al patent. This patent, however, describes in more detail the method for handling and transporting gasified ice to a desired point of liberation under atmospheric pressure while maintaining it at a temperature below its melting point. Again, the product is of the type described in the other two Barnes et al patents and is made by a process which would be extremely difficult to employ on a commercial scale.
Alder et al in U.S. Pat. No. 3,220,204 stated that while the prior art procedures of Barnes et al produce products which retain significantly high levels of carbonation during frozen storage, they noted that the products had a tendency to explode or pop (i.e., break apart and disintegrate with a loud noise) at an unpredictable point of time during dissolution. They indicated that when the Barnes et al carbonated ice products were added to water or milk, they frequently exploded in the glass. Products of this type have extremely limited commercial value.
Their solution to the problem entailed providing a high liquid-surface-to-gas contact during preparation of the hydrate. To achieve this, they employed a thin film of water which was subjected to carbon dioxide gas at a pressure and temperature above the eutectic point of the water and at a temperature low enough to form a hydrate. A suspension of hydrate in aqueous liquid was then transferred to a freezing zone and was converted to a stable form by freezing at a temperature below -3.degree. C. After freezing, the product was then removed from the molds and cut into sections of the desired length. Our experience has shown that products prepared in this manner would not only require added equipment, energy and time to transfer the product from a reactor to a freezing chamber, but that demolding or removing the product from the freezing chamber was also a source of difficulty. Typically, removing the product from the freezing chambers requires briefly heating the exterior surface of the chamber to melt the outer surface of the product to permit the cylindrical shape to be removed. This required added energy costs in that it is necessary to heat the cooled mold for demolding and then recool the mold for the next freezing operation. Additionally, this procedure has the disadvantage that carbon dioxide is released during heating.
In U.S. Pat. No. 3,255,600 to Mitchell et al, there is disclosed a process for forming carbonated ice wherein liquid carbon dioxide and liquid water are mixed under controlled conditions to form the carbonated ice product. The inventors indicate that they have discovered that liquid carbon dioxide results in a more rapid formation of the product while permitting more accurate control of the operating conditions. It has been our experience, however, that the use of liquid carbon dioxide requires the use of great quantities of energy and produces a product which has the popping and cracking problems associated with the earlier prior art.
As disclosed in Mitchell et al in U.S. Pat. No. 3,333,969, the problem of uneven release of carbon dioxide has persisted throughout this evolution of gasified ice products. They indicate that an important problem present in the handling and use of carbonated ice, particularly in the lower portion of the 10 to 118-volume range, was the uneven release of carbon dioxide from carbonated ice. They stated that this problem manifested itself in minor explosions or popping which, while not of a dangerous nature, where the gas is carbon dioxide, but may disturb the user and splatter the liquid in which it is placed. Mitchell et al propose subdividing carbonated ice into discrete particles while maintaining the temperature of the ice below 0.degree. C., and then compacting the discrete particles to form them into adhered mass or briquette. Briquetting did produce a gasified ice product having a commercially-satisfactory mechanical strength in the frozen state and also liberated entrained gas bubbles which are believed to cause the undesirable, spontaneous popping and exploding phenomena; however, because of the density of the starting gasified ice products, subdividing required large amounts of mechanical work and resulted in significant losses in carbon dioxide.
It is apparent from the foregoing discussion of the prior art that the problem of uneven and sometimes explosive release of gas from gasified ice products have troubled those skilled in the art. While the earlier patents indicated that the problem was particularly acute with regard to products containing high volumes of carbon dioxide or other gases, the later prior art indicated that the problem also persisted with regard to lower, more moderate gas-containing products.
Moreover, all of the prior art procedures have required high shear mechanical mixing or the use of more complicated equipment to obtain gas contact with a thin film of liquid to achieve the desired high level of gas liquid contact. Employing procedures of this type required large amounts of energy to be expended in imparting the necessary amount of mechanical work. Additionally, the disclosed techniques for freezing the resulting gas hydrate suspensions and removing them from the chamber in which they were frozen, whether it be the reaction vessel or another vessel, was also more complicated than would be desired.
Thus, there remains a definite need for an efficient, economical process which enables the production of a gasified ice product having a satisfactory level of gas content; which remains stable during storage, yet releases the gas rapidly upon melting in an aqueous liquid without popping or splashing.